The present invention relates to mining machines, and more particularly to a drive structure for rotating a non-oscillating mining head that is disposed transverse to the forward motion of the mining machine.
A typical continuous mining machine has a mining head at the front end for cutting and breaking the material from the mine face. A gathering head is usually disposed below the mining head to collect the mined material and feed it to a conveyor which conveys it to the rear of the mining machine. From the rear of the machine the mined material is discharged to a haulage vehicle or other equipment which takes the material away from the place of the mining operation. The mining head is typically driven by electric motors connected to the head by appropriate drive gears. A cutting or trim chain has typically been used to cut a path for the gear case and support arms which connect the mining head to the forward end of the mining machine.
The cutting chain or trim chain used on present day mining machines has evolved from the cutting chain originally used on cutter bars for conventional mining operations. The original cutter chains were mounted on a cutter bar that extended forwardly from the machine. And the cutter chain extended around the perimeter of the bar forming an orbital path. The cutter chain and bar were used to cut a narrow slot in the coal face as a preliminary step before drilling and shooting the coal.
Many inventions have been directed at designing cutter bits to withstand the force of cutting. Other inventions have had as their principal object the avoidance of entrapment or build up of coal dust between the sprocket teeth and the chain elements. Such build up causes the chain to ride around its sprocket at a diameter greater than the pitch diameter, thus producing excessive tensional forces on the chain.
The chains used on the present continuous non-oscillating drum type mining machines have encountered similar problems. Although the power to the cutter head is supplied by electric motors through appropriate gear transmissions, and although the chains have been used primarily to cut a path for the gear case, the chains have suffered the same problems of dust and dirt build up. U.S. Pat. No. 3,305,273 discloses one such attempt to avoid the dirt build up. In that patent the sprockets work against the outer ends of the chain pins. The pins fit between teeth, but one side is open so that the dirt or dust has a better chance to get away from the chain. In subsequent mining machine designs the trim chain has been eliminated altogether by extending the outer casing of the cutter drum over the centrally located gear case. However, extending the cutter drum casing in a cantilever method over the gear case has created other problems. The rotary drum is now more difficult to repair and maintain because it is now more difficult to remove it.